Most internal combustion engines have some type of an ignition circuit to generate a spark in the cylinder. The spark causes combustion of the fuel in the cylinder to drive the piston and the attached crankshaft. Typically, the engine includes a plurality of permanent magnets mounted on the flywheel of the engine and a charge coil mounted on the engine housing in the vicinity of the flywheel. As the flywheel rotates, the magnets pass the charge coil. A voltage is thereby generated on the charge coil and this voltage is used to charge a high voltage capacitor. The high voltage charge on the capacitor is released to the ignition coil by way of a triggering circuit so as to cause a high voltage, short duration electrical spark to cross the spark gap of the spark plug and ignite the fuel in the cylinder. This type of ignition is called a capacitive discharge ignition.
The design of standard reciprocating internal combustion engines which use spark plugs and ignition coils to initiate combustion have, for years, utilized combustion chamber shapes and spark plug placements which were heavily influenced by the need to reliably initiate combustion using only a single short-duration spark of relatively low intensity. In recent years, however, increased emphasis has been placed on fuel efficiency, completeness of combustion, exhaust cleanliness, and reduced variability in cycle-to-cycle combustion. This emphasis has meant that the shape of the combustion chamber must be modified and the ratio of the fuel-air mixture changed. In some cases, a procedure has been used which deliberately introduces strong turbulence or a rotary flow to the fuel-air mixture at the area where the spark plug electrodes are placed. This often causes an interruption or "blowing out" of the arc. This has placed increasing demands on the effectiveness of the combustion initiation process. It has been found highly preferable, in such applications, to have available an arc which may be sustained for as much as 4 to 5 milliseconds. Efforts to effectuate this idea have resulted in various innovations identified in several patents.
For example, U.S. Pat. No. 5,806,504, issued on Sep. 15, 1998 to French et al., teaches an ignition circuit for an internal combustion engine in which the ignition circuit includes a transformer having a secondary winding for generating a spark and having first and second primary windings. A capacitor is connected to the first primary winding to provide a high energy capacitive discharge voltage to the transformer. A voltage generator is connected to the second primary winding for generating an alternating current voltage. A control circuit is connected to the capacitor and to the voltage generator for providing control signals to discharge the high energy capacitive discharge voltage to the first primary winding and for providing control signals to the voltage generator so as to generate an alternating current voltage.
U.S. Pat. No. 4,998,526, issued on Mar. 12, 1991 to K. P. Gokhale teaches an alternating current ignition system. This system applies alternating current to the electrodes of a spark plug to maintain an arc at the electrodes for a desired period of time. The amplitude of the arc current can be varied. The alternating current is developed by a DC-to-AC inverter that includes a transformer that has a center-tapped primary and a secondary that is connected to the spark plug. An arc is initiated at the spark plug by discharging a capacitor to one of the winding portions at the center-tapped primary. Alternatively, the energy stored in an inductor may be supplied to a primary winding portion to initiate an arc. The ignition system is powered by a controlled current source that receives input power from a source of direct voltage, such as a battery on the motor vehicle.
In each of these prior patents, the devices use dual mechanisms in which a high-energy discharge is supplemented with a low-energy extending mechanism. The method of extending the arc, however, presents problems to the end user. First, the mechanism is, by nature, electronically complex in that multiple control mechanisms must be present either in the form of two separate arc mechanisms or by an arc mechanism and several specialized electronic drivers. Secondly, no method is presented for automatically sustaining the arc under a condition of repeated interruptions. Additionally, these mechanisms do not necessarily provide for a single functional-block unit of low mass and small size which contains all of the necessary functions within.
It is an object of the present invention to provide an ignition system which includes a transformer which is of a small enough size to be mounted directly on the spark plug.
It is a further object of the present invention to provide an ignition system which allows for simple radio frequency shielding so as to prevent radio frequency interference in the electrical system of the vehicle.
It is another object of the present invention to provide an ignition system which delivers constant wattage throughout the entire burn time.
It is still a further object of the present invention to provide an ignition system which enhances the ability to fire cold fuel at startup.
It is a further object of the present invention to provide an ignition system which delivers alternating current to the spark plug so as to greatly reduce spark plug gap erosion.
It is a further object of the present invention to provide an ignition system which provides for an adjustable arc duration on the electrode of the spark plug.
It is still a further object of the present invention to provide an ignition system which can be used consistently and effectively with variable input voltage from the vehicle battery.
It is still a further object of the present invention to provide an ignition system which includes means for sensing the voltage and current at the output of the ignition module for the purpose of assessing conditions within the cylinder.
It is still a further object of the present invention to provide an ignition system which is easy to use, easy to manufacture and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.